Modern wind turbines are either horizontal axis turbines or vertical axis turbines. Horizontal axis wind turbines dominate the market world wide. They normally have a nacelle, rotor and blades that sit on top of a tower. The nacelle consists of the generator, planetary gearing and all the control systems necessary to operate the turbine. The rotor holds the blades (usually 3) in their positions while they rotate around the main shaft in the nacelle. These wind turbines work for many years with little maintenance; however, they are very expensive. The economics of horizontal axis wind turbines have been improving, but subsidies are still needed in most parts of the world to be an economical energy alternative.
The vertical axis lift type wind turbines (excluding drag-type turbines) such as the darrieus-type rotor, gyro rotors, or the H-style turbines, have had moderate success. These turbines tend to have lower overall power efficiency and have little advantage over the dominant horizontal axis turbines. These turbines, however, do not need to be turned into the wind, they tend to be quieter and they have few moving parts.
Most turbines, whether horizontal or Vertical axis, typically need towers to raise the turbines high above the ground surfaces where the wind velocity is much higher and therefore more beneficial. The towers are an expensive component and in most cases they limit the size of the turbine.
PCT/CA2008/000678 by Lux discloses a lift-type or modified darrieus-type turbine with three or more blades at circumferentially spaced positions about the turbine rotor in which a plurality of support members are connected between adjacent ones of the blades in a generally circumferential direction about a full circumference of the rotor. The generally circumferential support members are described as being advantageous for optimally pre-stressing the blades and providing support to the blades against centrifugal forces. To minimize the drag, all of the support members are described as being horizontal in orientation between adjacent blades; however in this instance a large number of support members may be required and additional diametrically extending supports may be required to adequately support the blades.